The present invention relates to cutting elements of the type which are mounted on rotary drill bits for cutting through earth formations including rock formations, cement, plugs, etc.
Rotary drilling operations in earth formations are typically carried out using a rotary drill bit which is simultaneously rotated and advanced into the formation. Cutting is performed by cutting elements mounted on the drill bit, and the cuttings are flushed to the top of the borehole by the circulation of drilling fluid.
A conventional cutting element may comprise a cutting blank mounted on a cemented carbide stud. The blank includes a diamond disk disposed on a carbide substrate. The blank can be braze bonded to an inclined mounting face of the stud, and the stud 18 is then secured, e.g., by press-fit, shrink-fit, or brazing in a recess of the drill bit. Cutting elements of this type are disclosed, for example, in Rowley et al U.S. Pat. No. 4,073,354; Rohde et al U.S. Pat. No. 4,098,363; and Daniels et al U.S. Pat. No. 4,156,329. During the use of cutting elements of this type, cutting takes place by means of a section of the peripheral edge of the blank which is brought into contact with the formation being cut.
The stud is typically formed of a relatively ductile material such as steel or a hard substance such as a refractory carbide. The use of steel is advantageous in that it is resistant to fracture and bonds readily to the blank. On the other hand, due to its ductility, steel may not exhibit sufficient rigidity to prevent the diamond disc from breaking. That is, during a cutting operation the cutting forces acting reactively against the cutting elements will cause the ductile steel stud to deform to a greater extent than the hard diamond/carbide cutting blank. Such disparities in the amounts of deformation can cause the diamond layer to break.
Studs formed of refractory carbide are much harder and stiffer than steel, so there is less of a tendency for the diamond layer to break. However, cemented carbide is susceptible to fracture; cracks formed during a cutting operation may propogate completely thrugh the carbide, causing the stud to break apart. Also, when the blank is brazed to the mounting face of the stud, there can occur a loss of metal binder from the mounting face of the stud, thereby weakening that face and rendering it even more susceptible to fracture.
It is an object of the present invention to minimize or obviate problems of the type discussed above.
Another object is to provide a stiff, fracture-resistant stud which is highly resistant to erosion and wear and which effects a dependable bond with the blank.